Common Lisp differs from mathematics on some naming issues. In mathematics,
the set of real numbers is traditionally described as a subset of the
complex numbers, but in Common Lisp, the typereal and the typecomplex are
disjoint. The Common Lisp type which includes all mathematical complex
numbers is called number. The reasons for these differences
include historical precedent, compatibility with most other popular
computer languages, and various issues of time and space efficiency.